CTE-matched heat pipe

ABSTRACT

Heat sinks having a mounting surface with a coefficient of thermal expansion matching that of silicon are disclosed. Heat pipes having layered composite or integral composite low coefficient of expansion heat sinks are disclosed that can be mounted directly to silicon semiconductor devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending U.S. patentapplication Ser. No. 10/924,586, filed Aug. 24, 2004, which is itself acontinuation application of U.S. patent application Ser. No. 10/458,168,filed Jun. 10, 2003, now issued as U.S. Pat. No. 6,793,009, and is alsorelated to U.S. Provisional Patent Applications Nos. 60/561,436, filedApr. 12, 2004, and 60/574,158, filed May 25, 2004.

FIELD OF THE INVENTION

The present invention relates to heat sinks having mounting surfaces forsemiconductors, and more particularly to such heat sinks which includeone or more mounting surfaces having a coefficient of thermal expansionthat matches or nearly matches silicon.

BACKGROUND OF THE INVENTION

It is known that certain classes of semiconductor devices consumesubstantial amounts of power, which results in excess thermal energythat then must be transferred to the ambient environment. This wasteheat is typically communicated through a variety of thermal interfaces,heat spreaders, and structural elements prior to being rejected into theambient atmosphere by a heat sink. Since heat is often dissipated toroom temperature air, and the silicon constructed semiconductor has afinite upper bound on its operating temperature, package-related thermalresistance is becoming a limiting factor in the ability to dissipate thewaste heat.

The removal of package elements and interfaces will reduce packagethermal resistance, and allow the semiconductor device to either runcooler or dissipate more power. However, many of these elements arerequired in order to provide a match between the relatively lowcoefficient of thermal expansion (CTE) of silicon and the relativelyhigh CTE of the metal comprising the heat sink, rather than for bestthermal performance. This match needs to be maintained in order toprevent build-up of stress, as well as subsequent damage due to failureof the relatively brittle silicon component. Thus, there are thecompeting structural requirements of providing a layer of material toprovide a CTE match while at the same time needing to bring the heattransfer structure into intimate physical contact with the heatgenerating structure.

Matching may be achieved by at least two methods: the use of an alloysubstrate such as copper/tungsten whose CTE matches or nearly matchesthat of the silicon, or through the use of a ductile braze alloy betweenthe silicon and the remaining package elements. Either method preventstransmission of stresses due to mismatched CTE through the interface tothe silicon device. Some disadvantages of the alloy substrate includeexpense, unfavorable machining and stamping characteristics, and afairly low thermal conductivity. Some disadvantages of the ductile brazealloy include a limited fatigue life, which eventually results infailure due to delamination of the joint. This tendency is exacerbatedby the service conditions of most high power devices. Such devicesalmost always operate under conditions of periodic fluctuatingelectrical load, which leads to periodic fluctuations in thermal loadand mechanical stresses in the joint.

An alternative method involves the use of direct bond copper (DBC)aluminum nitride (AIN) in sheet form. This material is a “sandwich”comprised of a single layer of aluminum nitride and two outer layers ofOFE copper foil. The copper layers are first oxidized, and then pressedagainst the AIN at high temperature in a neutral atmosphere. Thisprocess causes the oxide to diffuse into the AIN and bonds the coppersheets tightly to the AIN inner layer. Since the copper layers arerelatively thin and are in an annealed state due to the high processingtemperature, the CTE of the resulting assembly is largely governed bythat the of the AIN.

None of the foregoing techniques have been found to be completelysatisfactory or have been successfully applied to heat pipe coolingdevices.

SUMMARY OF THE INVENTION

The present invention provides a heat transfer device including at leastone wall comprising a layered-composite comprising a first layer ofmaterial comprising a CTE that is substantially similar to a CTE ofsilicon that is disposed therebetween, and directly engaging secondlayers of material comprising a CTE greater than the silicon CTE.

In one embodiment, a heat transfer device is provided having a solidcold-plate base having a through-opening defined through it. Alayered-composite insert is hermetically received within thethrough-opening so as to be thermally and mechanically engaged with thebase so as to close the through-opening. The layered composite insertcomprises a layer of molybdenum disposed between and directly engaginglayers of OFE copper.

In another embodiment, a heat pipe is provided including a body havingan interior wall that defines a central passageway and at least one openend. A wick is disposed on at least a portion of the interior wall and aworking fluid saturates a portion of the wick. A layered-compositecold-plate base is provided that hermetically seals the at least oneopen end of the central passageway. The layered composite base comprisesa first layer of material comprising a CTE that is substantially similarto a CTE of silicon disposed between and directly engaging second layersof material comprising CTE greater than the silicon CTE.

In a further embodiment, a heat pipe is provided that includes a tubularbody having a central passageway with a wick disposed on at least anevaporator portion of the central passageway. The wick is at leastpartially saturated with a working fluid. A layered composite low CTEbase seals off the evaporator portion of the central passageway. Thelayered composite low CTE base comprises a layer of material selectedfrom the group consisting of aluminum nitride, molybdenum, and graphite.The layered composite low CTE base also includes a top surface and abottom surface comprising a material selected from the group consistingof copper, copper alloys, nickel, and nickel alloys.

In yet another embodiment, a heat pipe is provided that includes a bodydefining an interior a chamber with at least one wall of the bodycomprising a layered-composite. The layered composite wall preferablycomprises a first layer of material comprising a CTE that issubstantially similar to a CTE of silicon disposed between and directlyengaging second layers of material comprising CTE greater than thesilicon CTE. A wick is disposed on portions of the body that define theinterior chamber, with a working fluid saturating portions of the wick.

In another alternative embodiment, a heat pipe is provided that includesa body defining an interior a chamber including at least one wallcomprising a layered-composite of molybdenum disposed between layers ofOFE copper foil. A wick is disposed on portions of the body that definethe interior chamber, and a working fluid saturates portions of thewick.

In a further alternative embodiment, a heat pipe for spreading heat isprovided including a boundary structure including spaced-apart first andsecond plates that define an enclosed vapor chamber wherein the firstand second plates have a wick disposed upon the interior surfaces thatdefine the chamber. An opening is defined through the first plate. Alayered-composite insert is positioned within and hermetically sealingthe opening so as to be thermally and mechanically engaged with thefirst plate, wherein the layered composite insert comprises a layer ofmolybdenum disposed between and directly engaging layers of OFE copperfoil. A working fluid saturates the wick.

In another alternative embodiment, a heat pipe for spreading heat isprovided that includes a boundary structure including spaced-apart firstand second plates that define an enclosed vapor chamber. An opening isdefined through the first plate, and a layered-composite insert ispositioned within and hermetically seals the opening so as to bethermally and mechanically engaged with the first plate. The layeredcomposite insert comprises a layer of molybdenum disposed between anddirectly engaging layers of OFE copper foil. A wick is disposed oninterior portions of at least one of the first and second plates, and aworking fluid saturates a portion of the wick.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bemore fully disclosed in, or rendered obvious by, the following detaileddescription of the preferred embodiments of the invention, which are tobe considered together with the accompanying drawings wherein likenumbers refer to like parts and further wherein:

FIG. 1 is a partly exploded, elevational view of a CTE-matched heat pipeformed in accordance with one embodiment of the present invention;

FIGS. 2-4 are cross-sectional perspective views of the CTE-matched heatpipe of FIG. 1;

FIG. 5 is a broken-away cross-sectional view of a portion of the low CTEbase illustrated in FIGS. 2-4;

FIG. 6 is a perspective view of a composite base comprising a high CTEportion and a complementary low CTE insert portion positioned forplacement within an opening;

FIG. 7 is an exploded cross-sectional view of a composite base, as takenalong lines 7-7 in FIG. 6;

FIG. 8 is a cross-sectional view of the assembled composite base shownin FIG. 7;

FIG. 9 is a cross-sectional view of another embodiment of composite basehaving a wick applied to a surface of a low CTE insert portion;

FIG. 10 is a cross-sectional view of yet another embodiment of compositebase having a wick overlying a low CTE insert portion;

FIG. 11 is a cross-sectional view of a further embodiment of aCTE-matched base;

FIG. 12 is a cross-sectional view of tower heat pipe having a low CTEcomposite insert positioned within a high CTE base;

FIG. 13 is a perspective view of another embodiment of composite basehaving a plurality of low CTE inserts;

FIG. 14 is a perspective view of a planar heat pipe heat spreader formedin accordance with another embodiment of the present invention;

FIG. 15 is a cross-sectional view of the embodiment of composite baseshown in FIG. 14, as taken along lines 15-15 in FIG. 14;

FIG. 16 is an enlarged view of the cross-section shown in FIG. 15;

FIG. 17 is a perspective view of a planar heat pipe comprising acomposite wall formed in accordance with another embodiment of theinvention;

FIG. 18 is a cross-sectional view of the planar heat pipe shown in FIG.17, as taken along lines 19-19 in FIG. 17;

FIG. 19 is an enlarged cross-sectional view of the interior wallstructures of a planar heat pipe formed in accordance with the presentinvention;

FIG. 20 is a perspective view of a planar heat pipe comprising acomposite wall formed in accordance with another embodiment of theinvention;

FIG. 21 is a cross-sectional view of the planar heat pipe shown in FIG.20, as taken along lines 21-21 in FIG. 20;

FIG. 22 is an enlarged cross-sectional view of the interior wallstructures of a planar heat pipe formed in accordance with the presentinvention;

FIG. 23 is a perspective view of a planar heat pipe comprising acomposite wall and a low CTE insert formed in accordance with anotherembodiment of the invention;

FIG. 24 is a cross-sectional view of the planar heat pipe shown in FIG.23, as taken along lines 24-24 in FIG. 23;

FIG. 25 is an enlarged cross-sectional view of the interior wallstructures of a planar heat pipe formed in accordance with the presentinvention;

FIG. 26 is a perspective view of a planar heat pipe comprising acomposite wall and a low CTE insert formed in accordance with anotherembodiment of the invention;

FIG. 27 is a cross-sectional view of the planar heat pipe shown in FIG.26, as taken along lines 27-27 in FIG. 26;

FIG. 28 is an enlarged cross-sectional view of the interior wallstructures of a planar heat pipe formed in accordance with the presentinvention;

FIG. 29 is a cross-sectional view of yet a further embodiment of aplanar heat pipe having a composite wall structure formed in accordancewith the present invention; and

FIG. 30 is an enlarged cross-sectional view of the interior wallstructure of a planar heat pipe formed in accordance with the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This description of preferred embodiments is intended to be read inconnection with the accompanying drawings, which are to be consideredpart of the entire written description of this invention. The drawingfigures are not necessarily to scale and certain features of theinvention may be shown exaggerated in scale or in somewhat schematicform in the interest of clarity and conciseness. In the description,relative terms such as “horizontal,” “vertical,” “up,” “down,” “top” and“bottom” as well as derivatives thereof (e.g., “horizontally,”“downwardly,” “upwardly,” etc.) should be construed to refer to theorientation as then described or as shown in the drawing figure underdiscussion. These relative terms are for convenience of description andnormally are not intended to require a particular orientation. Termsincluding “inwardly” versus “outwardly,” “longitudinal” versus “lateral”and the like are to be interpreted relative to one another or relativeto an axis of elongation, or an axis or center of rotation, asappropriate. Terms concerning attachments, coupling and the like, suchas “connected” and “interconnected,” refer to a relationship whereinstructures are secured or attached to one another either directly orindirectly through intervening structures, as well as both movable orrigid attachments or relationships, unless expressly describedotherwise. The term “operatively connected” is such an attachment,coupling or connection that allows the pertinent structures to operateas intended by virtue of that relationship. In the claims,means-plus-function clauses are intended to cover the structuresdescribed, suggested, or rendered obvious by the written description ordrawings for performing the recited function, including not onlystructural equivalents but also equivalent structures.

Referring to FIGS. 1-4, a CTE-matched heat pipe 5 formed in accordancewith one embodiment of the present invention includes a body 8, a wick12, a working fluid 13, and a base 15. More particularly, body 8 maycomprise a cylindrical tube formed from a highly thermally conductivemetal, e.g., copper or its alloys or nickel or its alloys such as monel(an alloy of nickel and copper) which could be incorporated into thestructure with no significant changes in design or fabrication method. Avapor space is defined by a central passageway 20 extending along thelongitudinal axis of body 8. Body 8 includes a bottom end 22 and a topend 24. Top end 24 is pinched off or otherwise sealed at a fill tube 26during manufacture. Wick 12 is preferably formed from a brazed copperpowder that is distributed throughout the inner surface of body 8 thatdefines central passageway 20 at bottom end 22. Although not preferred,wick 12 may be distributed throughout the inner surface of body 8 at topend 24, and may also comprise adjacent layers of screening or a sinteredpowder structure with interstices between the particles of powder,having an average thickness of about 0.1 mm to 1.0 mm.

In one preferred embodiment of the present invention, no wick structureis present at top end 24 (the condenser region of heat pipe 5). This isdue in large part to the fact that gravity will drive the return ofcondensed working fluid 13 in the particular orientation shown in FIGS.1-4. A wick structure may be incorporated in top end 24, i.e., in thecondenser region of heat pipe 5, in order to provide return ofcondensate when the evaporator portion of the heat pipe is oriented soas to be above the condenser region. A wick structure in top end 24 mayalso reduce the temperature drop associated with condensation, as wellas improve performance of the device, even when the wick is not requiredto return the working fluid.

Wick 12 may also include a screen or grooves integral with the innersurface of body 8. Also, a plastic-bonded wick in the evaporator andcondenser regions of heat pipe 5 may be produced simultaneously and as acontiguous structure after body 8 is brazed to base 15. This wouldprovide a contiguous fluid conduit between the evaporator and condenserregions of heat pipe 5, which is advantageous when the evaporator iselevated. This feature may be met with a screen wick by “pushing” thescreen wick into an annular gap 28 located between bottom end 22 andbase 15.

Working fluid 13 may comprise any of the well known two-phasevaporizable liquids, e.g., water, alcohol, freon, methanol, acetone,fluorocarbons or other hydrocarbons, etc. CTE-matched heat pipe 5 isformed according to the invention by drawing a partial vacuum withinbody 8, and then back-filling with a small quantity of working fluid 13,e.g., just enough to saturate wick 12 just prior to final sealing ofbody 8 by pinching, brazing, welding or otherwise hermetically sealingfill tube 26, once base 15 is mounted to bottom end 22 of body 8. Theatmosphere inside heat pipe 5 is set by an equilibrium of liquid andvapor.

Base 15 comprises a plurality of layers of selected materials so as toform a layered-composite having a low CTE, i.e., a CTE that nearlymatches the CTE of a semiconductor, such as about 6.5 or less forsilicon (FIG. 1). For example, base 15 may be formed from a direct bondcopper (DBC) aluminum nitride. Base 15 may comprise a variety of shapesthat could be dictated by both the geometry of the semiconductor device30 that is to be cooled by CTE-matched heat pipe 5, or the shape ofbottom end 22 of body 8. Base 15 is fastened directly to bottom end 22of body 8 without the use of intermediate layers of CTE matchingmaterials or ductile brazes. A base 15 formed from DBC aluminum nitridepossesses several advantages that make it attractive for use as aninterface to silicon semiconductor devices and substrates. As nointerposing intermediate layers of CTE matching materials or ductilebrazes are needed, bottom end 22 of CTE-matched heat pipe 5 will bearranged in intimate thermal communication with semiconductor device 30.The interface between bottom end 22 and semiconductor device 30 willalso be significantly more resistant to thermal cycling and thermalfatigue. DBC aluminum nitride base 15 comprises high thermalconductivity, both in-plane and through-thickness, and its conductivityapproaches that of aluminum. Thus, the construction of the presentinvention allows bottom end 22 of CTE-matched heat pipe 5 to approachthe chip more closely, i.e., more closely than any method other thandirect die contact or direct liquid cooling, so that the package thermalresistance is as low as possible.

In another embodiment, base 31 may include a plurality of layers to forma layered-composite 38 comprising a layer of molybdenum 37 having a topsurface 39 and a bottom surface 40 (FIG. 5). A first layer 42 of OFEcopper foil is disposed over top surface 39 and a second layer 43 of OFEcopper foil is disposed over bottom surface 40 so as to formlayered-composite 38 (FIGS. 2-5). In this way, a layered composite isformed comprising a first layer 42 of relatively high CTE material(i.e., a CTE higher than that for silicon), a second layer 43 ofrelatively high CTE material (i.e., a CTE higher than that for silicon),and an intermediate layer 37 of relatively low CTE material, thusforming layered-composite 38 having an internal structure comprisinghigh CTE material/low CTE material/high CTE material. The CTE of such alayered-composite is often in a range from about 2.5 to about 10, with arange from about 3 to about 6.5 being preferred for most siliconapplications.

When the present invention comprises a layered-composite 38 formed fromlayers of copper/molybdenum/copper, a thickness ratio of 13%/74%/13% hasbeen found to provide adequate results. A copper/molybdenum/copperlayered-composite 38 comprises mechanical properties that are suitablefor higher temperature processing. This allows a silicon die to beattached to base 31, via soldering, without structural instability whichmay cause the silicon to crack or break.

Table 1 below presents thermal conductivity and CTE properties ofdifferent common materials that may be arranged as a layered-composite38 in conformance with the present invention. In tower applications, itis preferred that the high CTE layers of material be selected so thatbase 15 may be fastened directly to bottom end 22 of body 8 without theuse of any intermediate low CTE materials. Coefficient Thermal ExpansionMaterial (ppm/° C.) Silicon Carbide 2.6 Silicon 2.6 Molybdenum 4.9Graphite 5 Beryllium Oxide 8 Annealed Copper 16.4 Aluminum Nitride 3.680Mo20Cu 7.2 75W25Cu 10.2 33Cu/74Mo/33Cu 10 13Cu/74Cu/13Cu 6.5

A brazed wick 33 may be formed on the inner surface of base 15 or 31.Depending upon the heat load and particular power density, other wickstructures may be appropriate. Examples of such structures includescreen bonded to the heat input surface by spot-welding or brazing, amonolayer of powder metal, grooves cut in the copper layer of base 31,or an array of posts. Furthermore, it is also anticipated that aplastic-bonded wick may be substituted for the brazed copper wick.

In practice, semiconductor 30 is mounted to the bottom surface of base31. Heat from semiconductor 30 is conducted through base 31 into bottomend 22 of heat pipe 5. The heat causes working fluid 13 in wick 12 toevaporate. The vapor travels through central passageway 20 to condenserregion 35 of body 8. At condenser region 35, the vapor contacts theinner surface of body 8, condenses, and gives up its latent heat throughcondensation. Working fluid 13 then returns to bottom end 22 by eithergravity, or through the capillary action in a portion of wick 12 on theinner surface of body 8 at condenser 35.

As shown in FIGS. 1-4, fins 37 or other suitable extended surfaces maybe mounted to body 8 at condenser region 35 to convey the heat to theambient environment. It is anticipated that other fin types andstructures are possible, including a folded fin wrapped around acylindrical heat pipe envelope, an array of plate fins mounted radiallyaround the condenser, or an array of fins mounted to the top of thedevice.

Referring to FIGS. 6-12, a base 44 is also provided by the presentinvention in which a relatively low CTE layered-composite insert 45 ispositioned within a relatively high CTE cold plate 50, such as a copperplate. An opening 55 is formed within cold plate 50 that includes acounter-sunk region that provides an annular ledge 60 and asubstantially vertical wall 62 (FIGS. 6-8). Layered-composite insert 45is positioned within opening 55 and fixedly fastened in intimate thermalcommunication with annular ledge 60 and vertical wall 62 so as tocomplete base 44. Layered-composite insert 45 and cold plate 50 may bebonded together using conventional methods, such as brazing, soldering,adhesives, or direct bond attachment. Layered-composite insert 45comprises a plurality of layers wherein the layers may includeOFEcopper/aluminum nitride/OFEcopper, copper/molybdenum/copper, or evencopper/graphite (Table 1). In a preferred embodiment, layered-compositeinsert 45 includes an intermediate layer 37 of molybdenum, a top layer42 of copper and a bottom layer 43 of copper, and may be formed with aperiphery that conforms or is complementary to the geometric“foot-print” of semiconductor device 30, e.g., square, rectangular,circular or ellipsoidal, etc. When mounted, the surface of semiconductordevice 30 only makes thermal contact with a top mounting surface 47 oflayered-composite insert 45.

Referring to FIGS. 9-12, a capillary wick 33 may be formed on a surfaceof layered-composite insert 45. Also, layered-composite insert 45 may becomplementarily formed or machined so as to have a central prominence 48projecting upwardly into opening 55, thereby to improve engagement withannular ledge 60 and vertical wall 62 (FIG. 11). In this way, the top orbottom surfaces of layered-composite insert 45 may be arranged incoplanar relation with a top or bottom surface of cold plate 50. Ofcourse, central prominence 48 may project beyond the top or bottomsurfaces of any cold plate in order to form a land for engaging asemiconductor package. Also, wick 33 may be formed and arranged so as tooverlie the entire outwardly facing surface of layered-composite insert45 while only covering an adjacent potion of base 44. Of course, wick 33may be formed and arranged so as to overlie the entire surface oflayered-composite insert 45 and base 44.

Referring to FIG. 13, a base 87 may include a plurality oflayered-composite inserts 45 within a single high CTE cold plate 50.Each low CTE layered-composite insert 45 may be joined to cold plate 50in any one, or a combination of the foregoing fixation methods.

Referring to FIGS. 14-19 a planar heat pipe 100 may be formed inaccordance with the present invention having one or more walls thatcomprise at least one of a copper/molybdenum/copper or copper/aluminumnitride/copper layered-composite substantially similar in structure tothat of layered-composite portion 45. For example, a planar heat pipe100 may include a first plate 105 and a second plate 110 that arehermetically sealed at their respective peripheral edges so as to definea vapor chamber 112. Vapor chamber 112 is partially evacuated and backfilled with a suitable two-phase working fluid, e.g., water, Freon,ammonia, etc. A wick 120 is disposed upon one or more of the surfaces ofthe internally facing walls that together define vapor chamber 112.

In another embodiment of planar heat pipe 130 may be formed so as toinclude one or more layered-composite inserts 45 (FIGS. 20-28). Eitherfirst plate 105 or second plate 110 may define one or more openings thatare closed by the introduction of a layered-composite inserts 45.

Referring to FIGS. 29-30, a heat transfer base 135 comprises a firstplate 140 and a second plate 143 arranged to form a planar heat pipe.One or more openings in first plate 140 are hermetically sealed by theintroduction of a layered-composite insert 45. Each opening in firstplate 140 is formed within first plate 140 by a piercing or formingprocess so as to form an outwardly projecting, annular wall 147. In oneexample, high CTE cold plate 135 comprises a copper sheet that has beenpierced so as to draw an outwardly projecting, substantially annularwall 147 defining an outwardly facing, annular surface 150. Theperipheral top or bottom surface of layered-composite insert 45 isarranged so as to engage annular surface 150 of annular wall 147, andthe two are fixedly bonded to one another by any of the aforementionedconventional techniques, such as brazing, soldering, adhesives, ordirect bond attachment. Wick 33 may be formed within the closed recessin cold plate 135 that is defined by layered-composite 45 and annularwall 147.

It is to be further understood that the present invention is by no meanslimited only to the particular constructions herein disclosed and shownin the drawings, but also comprises any modifications or equivalentswithin the scope of the claims.

1. A heat transfer device comprising: at least one wall comprising a layered-composite comprising a first layer of material comprising a CTE that is substantially similar to a CTE of silicon disposed between and directly engaging second layers of material comprising CTE greater than said silicon CTE.
 2. A heat transfer device according to claim 1 wherein said first layer comprises molybdenum and said second layers comprise OFE copper foil.
 3. A heat transfer device according to claim 1 wherein said first layer comprises a CTE of about 10 or less.
 4. A heat transfer device according to claim 1 wherein said first layer comprises a CTE of about 6.5 or less.
 5. A heat transfer device according to claim 1 wherein said first layer is selected from the group consisting of aluminum nitride, molybdenum, and graphite.
 6. A heat transfer device according to claim 1 wherein said second layers are selected from the group consisting of copper, copper alloys, nickel, and nickel alloys.
 7. A heat transfer device according to claim 1 wherein said second layers are the same material.
 8. A heat transfer device according to claim 1 wherein said layered-composite is selected from the group consisting of copper/aluminum nitride/copper, copper/molybdenum/copper, and copper/graphite/copper.
 9. A heat transfer device comprising: a base defining a through-opening; and a layered-composite insert hermetically received within said through-opening so as to be thermally and mechanically engaged with said base and thereby to close said through-opening, wherein said layered composite insert comprises a layer of molybdenum disposed between and directly engaging layers of OFE copper.
 10. A heat pipe comprising: a body having an interior wall that defines a central passageway and at least one open end; a wick disposed on at least a portion of said interior wall; a working fluid; a layered-composite base that hermetically seals said at least one open end of said central passageway, wherein said layered composite base comprises a first layer of material comprising a CTE that is substantially similar to a CTE of silicon disposed between and directly engaging second layers of material comprising CTE greater than said silicon CTE.
 11. A heat transfer device according to claim 10 wherein said first layer comprises molybdenum and said second layers comprise OFE copper foil.
 12. A heat transfer device according to claim 10 wherein said first layer comprises a CTE of about 10 or less.
 13. A heat transfer device according to claim 10 wherein said first layer comprises a CTE of about 6.5 or less.
 14. A heat transfer device according to claim 10 wherein said first layer is selected from the group consisting of aluminum nitride, molybdenum, and graphite.
 15. A heat transfer device according to claim 10 wherein said second layers are selected from the group consisting of copper, copper alloys, nickel, and nickel alloys.
 16. A heat transfer device according to claim 10 wherein said second layers are the same material.
 17. A heat transfer device according to claim 10 wherein said layered-composite is selected from the group consisting of copper/aluminum nitride/copper, copper/molybdenum/copper, and copper/graphite/copper.
 18. A heat pipe comprising: a tubular body having a central passageway; a wick disposed on at least an evaporator portion of said central passageway; a working fluid; a layered composite low CTE base sealing off said evaporator portion of said central passageway, wherein said layered composite low CTE base comprises a layer of material selected from the group consisting of aluminum nitride, molybdenum, and graphite, and having a top surface and a bottom surface comprising a material selected from the group consisting of copper, copper alloys, nickel, and nickel alloys.
 19. A heat pipe comprising: a body defining an interior a chamber and including at least one wall comprising a layered-composite comprising a first layer of material comprising a CTE that is substantially similar to a CTE of silicon disposed between and directly engaging second layers of material comprising CTE greater than said silicon CTE; a wick disposed on portions of said body that define said interior chamber; and a working fluid.
 20. A heat transfer device according to claim 19 wherein said first layer comprises molybdenum and said second layers comprise OFE copper foil.
 21. A heat transfer device according to claim 19 wherein said first layer comprises a CTE of about 10 or less.
 22. A heat transfer device according to claim 19 wherein said first layer comprises a CTE of about 6.5 or less.
 23. A heat transfer device according to claim 19 wherein said first layer is selected from the group consisting of aluminum nitride, molybdenum, and graphite.
 24. A heat transfer device according to claim 19 wherein said second layers are selected from the group consisting of copper, copper alloys, nickel, and nickel alloys.
 25. A heat transfer device according to claim 19 wherein said second layers are the same material.
 26. A heat transfer device according to claim 19 wherein said layered-composite is selected from the group consisting of copper/aluminum nitride/copper, copper/molybdenum/copper, and copper/graphite/copper.
 27. A heat pipe comprising: a body defining an interior a chamber and including at least one wall comprising a layered-composite of molybdenum disposed between layers of OFE copper foil; a wick disposed on portions of said body that define said interior chamber; and a working fluid.
 28. A heat pipe for spreading heat comprising: a boundary structure including spaced-apart first and second plates that define an enclosed vapor chamber wherein said first and second plates have a wick disposed upon their interior surfaces that define said chamber; an opening defined through said first plate; a layered-composite insert positioned within and hermetically sealing said opening so as to be thermally and mechanically engaged with said first plate, wherein said layered composite insert comprises a layer of molybdenum disposed between and directly engaging layers of OFE copper foil; and a working fluid.
 29. A heat pipe for spreading heat comprising: a boundary structure including spaced-apart first and second plates that define an enclosed vapor chamber; an opening defined through said first plate; a layered-composite insert positioned within and hermetically sealing said opening so as to be thermally and mechanically engaged with said first plate, wherein said layered composite insert comprises a layer of molybdenum disposed between and directly engaging layers of OFE copper foil; a wick disposed on interior portions of at least one of said first and second plates; and a working fluid. 